1. Field of the Invention
The present invention relates to a toner used for image-forming methods such as an electrophotographic method, an electrostatic recording method and a toner jet method.
2. Description of the Related Art
In recent years, printers and copying machines are required to have high speed and low power consumption, and thus a toner is required to have an improved fixing performance. Specifically there is a requirement for realizing a toner that can be melted rapidly at a lower temperature and thus can be fixed rapidly with low energy and has excellent low-temperature fixability. At the same time, it is also required to realize heat-resistant storability devoid of the change in a toner such as solidification under a possible atmosphere of high temperature during transport of toner cartridges.
In order to meet the requirements, it has been considered to use a resin having a segment capable of forming a crystalline structure (hereinafter referred to as “crystalline resin”) as a binder resin. This utilizes a characteristic feature of crystalline resins, that is, a rapid decrease in viscosity at a melting point (sharp melting), thereby allowing a toner that does not change at a desired storage temperature and can be fixed at a low temperature due to sharp melting during fixation. Japanese Patent Application Laid-open Nos. 2012-255957, 2012-247657 and 2012-220569 propose toners containing crystalline polyesters.
However the above-mentioned toners may cause offset phenomenon in which the toner (particularly a crystalline resin having low viscosity) partially adheres to the surface of a fixing member such as a heat roller or a film and then is transferred to a subsequent transfer material. In order to address the problem, Japanese Patent Application Laid-open No. S62-273574 proposes use of crystalline and amorphous block resins as binder resins. This allows a toner to have reduced offsetting to a fixing member and stable fixing performance over a wide temperature range. Another disadvantage of the use of a crystalline resin is deterioration in durability. Crystalline resins generally have regularly-structured molecular arrangements and thus tend to be vulnerable to external force. Therefore the toner containing a crystalline resin in order to realize both low-temperature fixability and heat-resistant storability has problems of easy deterioration and generation of image defects such as streaks during continuous printing.